Abstract Complexation of 4-nitropyridine N-oxides with ν-(BF 3, HCl) and π-acceptors (tetracyanoethylene, chloranil, 2, 3-dichloro-5, 6-dicyano-1, 4-benzoquinone, 7, 7, 8, 8- tetracyanoquinodimethane) activates the nitro group to nucleophilic replacement by chlorine. Adducts formed by 4-nitropyridine and 4-nitroquinoline N-oxides with boron trifluoride and hydrogen chloride were studied by IR spectroscopy. It was shown that these ...